1. Field of the Invention
The present invention relates to a transparent conductive substrate for use with various types of display apparatuses and a display apparatus thereof.
2. Description of the Related Art
As technologies for satellite and mobile communications have advanced, light-weight display apparatuses for handy information terminal units have been developed. As substrates of the display apparatuses, transparent conductive substrates have been used.
A conventional transparent conductive substrate is constructed by forming a transparent electrode layer on a glass plate with a thickness of 0.7 to 1.1 mm. The glass plate has a heat resisting characteristic, a chemical resisting characteristic, and optical characteristics such as high light transmittance, low haze, and low retardation Since the transparent conductive substrate has a glass plate as a base, it can satisfactorily withstand a photo etching process and a sputtering process performed in an alignment film forming process and an electrode forming process that are performed in the fabrication of a liquid crystal display apparatus.
On the other hand, a handy information terminal unit should have a shock resisting characteristic and a light weight. However, when the thickness and weight of the glass plate are reduced, the shock resisting characteristic of the resultant plate becomes lower than that of the conventional glass plate. Thus, a technology for using plastics, which have high shock resisting characteristic and light weight, for a transparent conductive substrate has been required.
Thus far, many attempts for using plastic bases for liquid crystal display apparatuses have been made. To improve the display quality, transparent conductive substrates used for the liquid crystal display apparatuses should have for example an oxygen barrier characteristic, a steam barrier characteristic, and a scratch resisting characteristic. However, with only a plastic base, such characteristics cannot be accomplished.
To solve this problem, a method for forming a laminate of an oxygen barrier layer, a steam barrier layer, a hard coat layer as a protection layer for improving mechanical strength and chemical resisting characteristic, a variety of adhesive agent layers for improving adhesive characteristics between each layer, between the base and the adjacent layer, or between the transparent electrode layer and the adjacent layer and so forth on a plastic plate as a compound base for a transparent conductive substrate has been proposed. In this case, to form a transparent electrode layer an orientation film, the base should have a heat resisting characteristic.
However, the conventional plastic bases cannot satisfy both optical characteristics such as high light transmittance, low haze value, low retardation value, and so forth and high heat resisting characteristic that is required for the fabrication process of the transparent conductive substrate at the same time. In particular, both the high light transmittance and the high heat resisting characteristic cannot be satisfied at the same time. For example, to improve the heat resisting characteristic and thereby form a highly conjugated structure, an aromatic ring or a hetero ring is introduced in the main chain of a macromolecule compound that composes a plastic. In this case, the plastic is inevitably colored. Thus, the light transmittance of the visible portion is deteriorated. To improve the heat resisting characteristic, a high crystal structure is formed. In this case, the haze value and the retardation value increase. In consideration of both the high light transmittance and the high heat resisting characteristic, as examples of the plastic base, polycarbonate, polyarylate, polysulfone, polyethersulfone, and norbornene resin which has a norbornene structure are normally used. The thermally deforming temperatures of these materials are at most around 220.degree. C. Thus, the heat resisting characteristic and the light transmittance should be further improved.
In addition, when an oxygen barrier layer, a steam barrier layer, a hard coat layer, various adhesive agent layers, and so forth are laminated as a base, since the heat resisting characteristic of these layers is low, a fabrication process of which the material temperature exceeds 170.degree. C. cannot be used. From a view point of the heat resisting characteristics of such various protection layers, structures of which a metallic oxide thin film layer composed of SiOx, AlOx, or MgOx or a metallic nitride thin film layer composed of SiNx is formed as an oxygen barrier layer and a steam barrier layer on the base have been used (for example, Japanese Patent Laid-Open Publication Nos. 6-99536 and 63-112632, and U.S. Pat. No. 3,442,686).
These layers are formed by sputtering method, evaporation method, CVD method, or sol-gel method. In particular, when a metallic oxide thin film layer or a metallic nitride thin film layer that is free from a defect, they provide very good oxygen barrier characteristic and steam barrier characteristic. The oxygen barrier characteristic and the steam barrier characteristic of these layers are around 10 times higher than those of ethylene-vinylalcohol copolymer, polychloro vinylidene, or polypropylene. However, when the metallic oxide thin film layer or the metallic nitride thin film layer that have excellent barrier characteristics are densely formed, high temperatures are required in the crystallizing process. Thus, the required temperatures may exceed the heat resisting characteristic of the base.
Normally, to improve the adhesion of the base and the metallic oxide thin film layer or the metallic oxide thin film layer, a surface treatment is performed for the base. However, the effect of the surface treatment is not always satisfactory. To solve this problem, a protection layer composed of a thermoplastic resin is formed on the front surface of the metallic oxide thin film layer or the metallic nitride thin film layer. In addition, to improve the adhesion of the protection layer and an electrode material formed on the front surface thereof, an adhesive agent layer should be disposed between these layers. Alternatively, a proper surface process should be performed on the front surface of the protection layer. However, such an adhesive agent layer has a problem on the heat resisting characteristic. Thus, it is difficult to equally form a transparent electrode layers
As described above, although the transparent conductive substrate is important for reducing the thickness and weight of a display apparatus, the transparent conductive substrate that has the conventional plastic base cannot satisfy both the optical characteristics such as high light transmittance, low haze value, and low retardation value and high heat resisting characteristic in comparison with the transparent conductive substrate that has a conventional glass material.
In addition, from a view point of the thermal process environment, it is difficult to form a metallic oxide thin film layer or a metallic nitride thin film layer that satisfies the oxygen and steam barrier characteristics and scratch resisting characteristic.
Moreover, when the metallic oxide thin film layer or the metallic nitride thin film layer is formed, the adhesion of the base and such thin film layers and of a transparent electrode layer and such thin film layers is deteriorated.